Comparison of flexural properties of composite restoratives using the ISO and mini-flexural tests

The purpose of this study was to investigate the flexural properties (flexural strength and flexural modulus) of four commercial composite restoratives (Silux Plus, Z100, Ariston and Surefil) using the ISO 4049 flexural test (IFT) and a mini-flexural test (MFT). Both tests involved the use of three-point loading and the same fixture. The difference between the tests was in the length of the composites specimens and the distance between the supports [20 mm (IFT) and 10 mm (MFT)]. Six specimens were made for each material and flexural test. Test specimens [25 x 2 x 2 mm (IFT) and 12 x 2 x 2 mm (MFT)] were fabricated according to manufacturers' recommendations. After light-polymerization, the specimens were stored in distilled water at 37 degrees C for 24 h. The specimens were subsequently blotted dry, measured and subjected to flexural testing using an Instron Universal Testing Machine with a crosshead speed of 0.75 mm min(-1). Data was analysed using anova/Scheffe's, paired samples test (P < 0.05) and Pearson's correlation (P < 0.01). For both IFT and MFT, results of statistical analysis of flexural strength were identical. Silux had significantly lower flexural strength compared with the other composites and the flexural strength of Ariston was significantly lower than Z100 and Surefil. For IFT, the flexural modulus of Z100 was significantly higher than Silux, Ariston and Surefil while for MFT, Silux had significantly lower modulus compared with Z100, Ariston and Surefil. A significant, strong and positive correlation (r = 0.95) was observed for flexural strength between IFT and MFT. Correlation for flexural modulus was also significant and positive but was weaker (r = 0.53). As MFT has the advantage of ease of specimen fabrication and is more clinically realistic, it is suggested for the testing of composite restoratives. CLINICAL RELEVANCE: The mini-flexural test may be better than the ISO flexural test for screening of composite restoratives for clinical applications.     

Flexural strength and modulus of elasticity of different types of resin-based composites

The aim of the study was to test whether the filler composition of resin composites influences their flexural strength and modulus of elasticity. Flexural strength and modulus of elasticity were obtained through a three-point bending test. Twelve bar shaped specimens of 5 commercially available composites--Supreme (3M/ESPE), a universal nanofilled composite; Esthet-X (Dentsply), Z-250 (3M/ESPE), Charisma (Heraeus Kulzer), universal hybrid composites; and Helio Fill (Vigodent), a microfine composite--were confectioned according to the ISO 4049/2000 specifications. The test was performed after a 7-days storage time using a universal test machine with a crosshead speed of 1 mm/min. The filler weight content was determined by the ashing technique. The data obtained on the mechanical properties were submitted to ANOVA and Tukey test (p < 0.05). Pearson's correlation test was used to determine the correlation between the filler content and the mechanical properties. A weak but significant correlation between the mechanical properties evaluated and the filler weight content was observed (p < 0.000). The microfine composite presented the lowest filler weight and the lowest mechanical properties. Statistically different flexural strength and modulus of elasticity results were observed among the universal hybrid composites. The nanofilled composite presented intermediary results. Within the limitations of this in vitro study, it could be concluded that the filler content significantly interfered in the flexural strength and modulus of elasticity of the composites tested.     

Mechanical properties and wear behavior of light-cured packable composite resins.

OBJECTIVES: Determination of flexural strength, flexural modulus, fracture toughness and wear resistance of three packable composites (Solitaire, Surefil, ALERT) and a packable ormocer (Definite) in comparison with an advanced hybrid composite (Tetric Ceram) and an ion-releasing composite (Ariston pHc). METHODS: Flexural strength, flexural modulus and fracture toughness of each material were determined in three-point bending (each test n = 10). Single-edge notched-bend specimens were used to evaluate the fracture toughness (K1C). Wear of the materials (n = 8) was determined in a pin-on-block-design with a spherical Degusit antagonist at 50 N vertical load and quantified by a replica technique using a 3D-laser scanner. Replicas were made after 6000, 10,000, 30,000 and 50,000 load cycles. The mean wear rate (MWR (micron 3 cycle-1)) was obtained by a linear regression analysis in the steady-state of the time-wear-curve. All results were statistically analyzed with ANOVA and post hoc Tukey HSD tests (p < 0.05). RESULTS: ALERT exhibited the highest flexural modulus (12.5 +/- 2.1 GPa) and K1C (2.3 +/- 0.2 MN m-3/2), but the lowest wear resistance (8275 micron 3 cycle-1). Solitaire presented the highest wear resistance (1591 micron 3 cycle-1), but significantly lower flexural strength (81.6 +/- 10.0 MPa), flexural modulus (4.4 +/- 0.3 GPa), and K1C (1.4 +/- 0.2 MN m-3/2) than all other materials. Surefil revealed a significantly higher flexural modulus (9.3 +/- 0.9 GPa) and wear resistance (3028 micron 3 cycle-1) than Tetric Ceram (6.8 +/- 0.5 GPa; 5417 micron 3 cycle-1) and Ariston pHc (7.3 +/- 0.8 GPa; 7194 micron 3 cycle-1). SIGNIFICANCE: The tested packable composite resins differed significantly in their mechanical properties. This study suggested that fracture and wear behavior of the composite resins are highly influenced by the filler system. Overall, Surefil demonstrated good fracture mechanics parameters and a low wear rate.     

The effect of ceramic and porous fillers on the mechanical properties of experimental dental composites.

OBJECTIVES: The purpose of this study was to investigate the effect of ceramic fillers (containing leucite crystals) and their porosity on the mechanical properties of a new experimental dental composite in order to compare with the properties of composites containing conventional glass fillers. METHODS: In this study, experimental composites were prepared by mixing the silane-treated fillers with monomers. Experimental composites were divided into four groups according to their filler type, amount and porosity. The monomers were composed of 70% Bis-GMA and 30% TEGDMA by weight for all groups. Glass and leucite-containing-ceramic were prepared as different filler types. In order to make fillers porous, leucite-containing-ceramic fillers were treated with HF acid. Camphorquinone and DMAEMA were used as photo initiator system. Post-curing was done for all groups before mechanical testing. Degree of Conversion of composites was measured using FTIR spectroscopy. The diametral tensile strength (DTS), flexural strength and flexural modulus were measured and compared among the groups. RESULTS: The results showed that the stronger and more porous filler has a positive effect on flexural strength. Porosity of filler increased flexural strength significantly. No significant difference was found in DTS tests among the groups. Flexural modulus was affected and increased by using ceramic fillers. The type of the filler affected the DC of the composite and DC increased by post-curing. SIGNIFICANCE: Flexural strength is one of the most important properties of restorative dental materials. Higher flexural strength can be achieved by stronger and more porous fillers. Investigation into the effect of filler on dental material properties would be beneficial in the development of restorative dental material.     

The effect of filler loading and morphology on the mechanical properties of contemporary composites

STATEMENT OF PROBLEM: Little information exists regarding the filler morphology and loading of composites with respect to their effects on selected mechanical properties and fracture toughness. PURPOSE: The objectives of this study were to: (1) classify commercial composites according to filler morphology, (2) evaluate the influence of filler morphology on filler loading, and (3) evaluate the effect of filler morphology and loading on the hardness, flexural strength, flexural modulus, and fracture toughness of contemporary composites. MATERIAL AND METHODS: Field emission scanning electron microscopy/energy dispersive spectroscopy was used to classify 3 specimens from each of 14 commercial composites into 4 groups according to filler morphology. The specimens (each 5 x 2.5 x 15 mm) were derived from the fractured remnants after the fracture toughness test. Filler weight content was determined by the standard ash method, and the volume content was calculated using the weight percentage and density of the filler and matrix components. Microhardness was measured with a Vickers hardness tester, and flexural strength and modulus were measured with a universal testing machine. A 3-point bending test (ASTM E-399) was used to determine the fracture toughness of each composite. Data were compared with analysis of variance followed by Duncan's multiple range test, both at the P<.05 level of significance. RESULTS: The composites were classified into 4 categories according to filler morphology: prepolymerized, irregular-shaped, both prepolymerized and irregular-shaped, and round particles. Filler loading was influenced by filler morphology. Composites containing prepolymerized filler particles had the lowest filler content (25% to 51% of filler volume), whereas composites containing round particles had the highest filler content (59% to 60% of filler volume). The mechanical properties of the composites were related to their filler content. Composites with the highest filler by volume exhibited the highest flexural strength (120 to 129 MPa), flexural modulus (12 to 15 GPa), and hardness (101 to 117 VHN). Fracture toughness was also affected by filler volume, but maximum toughness was found at a threshold level of approximately 55% filler volume. CONCLUSION: Within the limitations of this study, the commercial composites tested could be classified by their filler morphology. This property influenced filler loading. Both filler morphology and filler loading influenced flexural strength, flexural modulus, hardness, and fracture toughness.     

Flexural strength and Weibull analysis of a microhybrid and a nanofill composite evaluated by 3- and 4-point bending tests.

OBJECTIVES: The aim of the present study was to evaluate the flexural strength and the Weibull modulus of a microhybrid and a nanofill composite by means of 3- and 4-point bending tests. METHODS: Thirty specimens of Filtek Z250 (3M/ESPE) and Filtek Supreme (3M/ESPE) were prepared for each test according to the ISO 4049/2000 specification. After 24h in distilled water at 37 degrees C the specimens were submitted to 3- and 4-point bending tests using a universal testing machine DL2000 (EMIC) with a crosshead speed of 1 mm/min. Flexural strength data were calculated and submitted to Student's t-test (alpha=0.05) and Weibull statistics. The fractured surfaces were analyzed based on fractographic principles. RESULTS: The two composites had equivalent strength in both test methods. However, the test designs significantly affected the flexural strength of the microhybrid and the nanofill composites. Weibull modulus (m) of Supreme was similar with both tests, while for Z250, a higher m was observed with the 3-point bending test. Critical flaws were most often associated with the specimen's surface (up to 90%) and were characterized as surface scratches/grooves, non-uniform distribution of phases, inclusions and voids. SIGNIFICANCE: Flexural strength as measured by the 3-point bending test is higher than by the 4-point bending test, due to the smaller flaw containing area involved in the former. Despite the large difference in average filler size between the composites, the volume fraction of the filler in both materials is similar, which was probably the reason for similar mean flexural strength values and fracture behavior.     

Microstructural characterization and fracture behavior of a microhybrid and a nanofill composite

OBJECTIVES: To characterize the microstructure and composition of two different composites, and to determine their influence on the physical properties and fracture behavior. METHODS: The microstructure and composition of a microhybrid (Filtek Z250-Z2) and a nanofill (Filtek Supreme-SU) composite were analyzed using scanning electron microscopy (SEM) and electron dispersive spectroscopy (EDS). Filler wt% was determined by thermogravimetric analysis. Hardness (H) and degree of conversion (DC) were evaluated at top and bottom surfaces of 2-mm thick specimens, and the dynamic elastic modulus (E) was determined with ultrasonic waves. Bar specimens (n=30) were subjected to flexure loading and flexural strength (sigmaf) was calculated (MPa). Fractographic analysis (FA) was performed to determine the fracture origin (c) for calculation of fracture toughness (KIc), and these results were compared to those from the single edge notch beam (SENB) method. Results were statistically analyzed using two-way ANOVA, Student's t-test and Weibull analysis (alpha=0.05). RESULTS: Z2 had higher filler wt%, H, E and DC at 2-mm depth as compared with SU. The fracture behavior (sigmaf and KIc) and the structural reliability (m) of the composites were similar. Results of KIc tested by SENB or calculated from fracture surfaces from flexure testing were similar. SIGNIFICANCE: The microstructural organization of the composites determines their physical properties, in spite of the similar filler content. In contrast, the microstructure did not influence the fracture behavior and the structural reliability of these highly filled composites. FA was shown to be a reliable method for determining the KIc of composites.     

Shear punch strength and flexural strength of model composites with varying filler volume fraction, particle size and silanation.

OBJECTIVE: The effect of filler volume fraction, particle size and silanation on shear punch strength, flexural strength and flexural modulus of model composites has been evaluated. METHODS: Hybrid type glass filled (0-65.2 vol%), composites some without filler silanation (30.7-51.0 vol%) and microfilled type (0-13.0 vol%) resin matrix (UDMA and EGDMA) composites (Shofu Inc., Japan) were used in the study. For the shear punch test, 10 disc specimens, 0.5mm thick and 9 mm diameter, were prepared for each composite and tested with a 3.2mm dia punch at 1.0mm/min. Flexural strength (n=10) was measured by the method outlined in ISO 4049. Data were analyzed using ANOVA and Fisher's multiple-range test. RESULTS: Shear punch strength and flexural strength increased with increasing filler content up to 52.2% for hybrid composites and between 0 and 9.1% for microfilled composites. Shear punch strength and flexural strength decreased with increasing filler volume fraction for un-silanated composites. Flexural modulus for all materials increased with increasing filler volume fraction. Hybrid composites with silanated fillers have significantly higher values of flexural strength, flexural modulus and shear punch strength than equivalent materials with un-silanated fillers. SIGNIFICANCE: The results showed that filler silanation is an important factor for determining material strength. Additions of small quantities of microfillers appeared to have a greater effect on shear strength than equivalent amounts of hybrid filler. The shear punch test may prove beneficial for routine testing of composites as specimen preparation was simple, specimen quality was easy to maintain and the results are meaningful.     

Influence of radiant exposure on contraction stress, degree of conversion and mechanical properties of resin composites.

OBJECTIVE: To verify the influence of radiant exposure (H) on contraction stress (CS), degree of conversion (DC) and mechanical properties of two restorative composites. METHODS: Filtek Z250 (3M ESPE) and Heliomolar (Ivoclar) were photoactivated with 6, 12, 24, or 36 J/cm2 at continuous irradiance of 600 mW/cm2. CS at 10 min was determined in a low compliance testing system. DC, flexural strength (FS), flexural modulus (FM) and Knoop microhardness (KHN) were measured after 24 h storage at 37 degrees C. KHN and DC measurements were conducted on the irradiated surface of 1mm thick disk-shaped specimens. Bar-shaped specimens were submitted to three-point bending to determine FS and FM. Data were analyzed by one-way ANOVA/Tukey's test (alpha = 0.05) separately for each composite. RESULTS: For Filtek Z250, no significant increase in CS was observed above 12 J/cm2. DC and FM were similar at all H values, while FS increased significantly between 6 and 24 J/cm2. KHN was significantly different among all H levels, except between 12 and 24 J/cm2. For Heliomolar, CS and KHN increased significantly with H, except between 24 and 36 J/cm2. DC, FM and FS did not vary, regardless of the radiant exposure. SIGNIFICANCE: Variables tested behaved differently. CS and KHN were more sensitive to increasing radiant exposures than the other properties evaluated. FS varied only for Filtek Z250, while, for both composites, DC and FM were not affected by different H values.     

Comparison between a plasma arc light source and conventional halogen curing units regarding flexural strength, modulus, and hardness of photoactivated resin composites

The plasma arc curing light Apollo 95 E (DMDS) is compared to conventional curing lights of different radiation intensities (Vivalux, Vivadent, 250 mW/cm²; Spectrum, DeTrey, 550 mW/cm²; Translux CL, Kulzer, 950 mW/cm²). For this purpose, photoactivated resin composites were irradiated using the respective curing lights and tested for flexural strength, modulus of elasticity (ISO 4049), and hardness (Vickers, Knoop) 24 h after curing. For the hybrid composites containing only camphoroquinone (CQ) as a photoinitiator (Herculite XRV, Kerr; Z100, 3 M), flexural strength, modulus of elasticity, and surface hardness after plasma curing with two cycles of 3 s or with the step-curing mode were not significantly lower than after 40 s of irradiation using the high energy (Translux CL) or medium energy conventional light (Spectrum). However, irradiation by only one cycle of 3 s failed to produce adequate mechanical properties. Similar results were observed for the surface hardness of the CQ containing microfilled composite (Silux Plus, 3 M), whereas flexural strength and modulus of elasticity after plasma curing only reached the level of the weak conventional light (Vivalux). For the hybrid composites containing both CQ and photoinitiators absorbing at shorter wavelengths (370–450 nm) (Solitaire, Kulzer; Definite, Degussa), plasma curing produced inferior properties mechanical than conventional curing; only the flexural strength of Solitaire and the Vickers hardness of Definite reached levels not significantly lower than those observed for the weak conventional light (Vivalux). The suitability of plasma arc curing for different resin composites depends on which photoinitiators they contain. Received: 5 July 1999 / Accepted: 16 March 2000     

Effect of LED and halogen light curing on polymerization of resin-based composites

The clinical performance of light polymerized resin-based composites (RBCs) is greatly influenced by the quality of the light curing unit (LCU). A commonly used unit for polymerization of RBC material is the halogen LCUs. However, they have some drawbacks. Development of new blue superbright light emitting diodes (LED LCU) of 470 nm wavelengths with high light irradiance offers an alternative to standard halogen LCU. The aim of this study is compared the effectiveness of LED LCU and halogen LCU on the degree of conversion (DC) of different resin composites [two hybrid (Esthet-X, Filtek Z 250), four packable (Filtek P60, Prodigy Condensable, Surefil, Solitaire), one ormocer-based resin composite (Admira)]. The DC values of RBCs polymerized by LED LCU and halogen LCU ranged approximately from 61.1 +/- 0.4 to 50.6 +/- 0.6% and from 55.6 +/- 0.7 to 47.4 +/- 0.5%, respectively. Significantly higher DC of RBCs except Surefil and Filtek Z 250 was obtained for LED LCU compared with halogen LCU (P < 0.05). Surefil and Filtek Z 250 exhibited no statistically significant difference values between LED LCU and halogen LCU (P > 0.05). As a result, it was observed that the performance of LED LCU used in the study was satisfactory clinically and had sufficient irradiance to polymerize RBCs (hybrid, packable and ormocer based) at 2 mm depth with a curing time of 40 s.     

Evaluation of welded titanium joints used with cantilevered implant-supported prostheses

STATEMENT OF PROBLEM: Early failure of laser-welded titanium implant frameworks in clinical practice has prompted an investigation of the strength and durability of welded cantilevered titanium sections. PURPOSE: The purpose of this study was to determine the effect that the use of filler wire in laser welding of titanium cantilever frameworks had on the flexural strength and fatigue resistance of the welded joints. MATERIAL AND METHODS: Sixty titanium implant-supported frameworks with 12-mm cantilevers were fabricated in 4 groups (n=15), using 3 different laser welding protocols with 0, 1, and 2 weld passes with filler wire, and 1 conventional tungsten inert gas welding method. The volume of filler wire used (mean volumes 0, 1.7, 3.4, and 8.3 mm(3)) was determined by measurement of the length of wire before and after welding each joint. Ten frameworks from each group were tested for ultimate flexural strength by loading the cantilevers 10 mm from the abutment. The remaining 5 frameworks from each group were similarly tested under a simulated masticatory load of 200 N until failure, or to 1 million cycles. A 2-way analysis of variance was used to examine the flexural strengths, and log-rank statistics were applied to cyclic test data (alpha=.05). RESULTS: There were significant differences between the 4 groups for ultimate flexural strength (P<.001) and resistance to cyclic loading (P=.002). The volume of filler wire added was a significant predictor of ultimate flexural strength (P=.03), and was a borderline determinant of the number of cycles to failure at 200 N (P=.05). Each laser weld pass with filler wire roughly doubled the ultimate flexural strength and fatigue resistance of the joint relative to the previous weld. Tungsten inert gas welding with efficient argon shielding deposited the most filler wire and produced the strongest and most fatigue-resistant joints. CONCLUSION: The ultimate flexural strength and fatigue resistance of cantilevered joints in laser-welded titanium prostheses are improved by the use of filler wire. Tungsten inert gas welding with efficient argon shielding can be used in situations when a high-strength joint is required.     

Influence of environmental conditions on dental composite flexural properties.

OBJECTIVE: To determine if increased relative humidity and temperature simulating intraoral environmental conditions adversely affect flexural properties of dental composites. METHODS: Specimen fabrication followed ANSI/ADA specification 27 for resin-based filling materials, except that ambient laboratory conditions (47% relative humidity at 22 degrees C) or simulated intraoral conditions (90% relative humidity at 35 degrees C) were used when fabricating and polymerizing specimens. Ten specimens were made of each of three commercially available composites at each condition. As per the specification, after aging specimens in 10 ml of deionized water at 37 degrees C for 24 h, flexural properties were measured using a 3-point bend test. RESULTS: A two-factor ANOVA and Fisher's least significant difference (LSD) post hoc (alpha=0.05) indicated there were significant differences in flexural modulus and strength as a function of material, with Z250=TPH>Prodigy. However, neither flexural modulus nor flexural strength of any material was adversely influenced by fabrication conditions. SIGNIFICANCE: Although the flexural properties did not decrease with respect to fabrication conditions, the flexural modulus of some of the materials (TPH Spectrum and Z250) increased when specimens were fabricated at simulated intraoral temperature and relative humidity. Thus, simulation of these factors may be important in laboratory testing, since the resultant properties may better reflect flexural properties associated with dental composite restorations placed clinically.     

Comparison of flexural properties and surface roughness of nanohybrid and microhybrid dental composites

Recently introduced nanohybrid dental composites have promised a smoother surface finish and strength, comparable to that of microhybrid composites. This study compared the mechanical properties and surface finish of nanohybrid and microhybrid composites by measuring the flexural strength and modulus (four-point bend) and surface roughness after polishing (using atomic force microscopy) of six commercial dental composites (three nanohybrid, three microhybrid). Scanning electron microscopy (SEM) was used to qualitatively characterize filler morphology and size. The flexural strength and modulus were significantly higher among the microhybrid composites, while the nanohybrid composites exhibited significantly lower surface roughness. SEM characterization revealed differences in filler particle size and shape that could affect the flexural properties and surface roughness. Composites containing spherical filler particles exhibited higher flexural properties and lower roughness values compared to composites with irregular fillers. These results did not support the premise that nanohybrid composites offer similar mechanical properties to microhybrids in addition to a better surface finish.     

Development of metal-resin composite restorative material. Part 3. Flexural properties and condensability of metal-resin composite using Ag-Sn irregular particles

Powder-liquid type metal-resin composites, using Ag-Sn irregular particles as the filler, 4-META as coupling agent and UDMA + TEGDMA as resin matrix, were experimentally prepared under 9 different conditions (three different particle sizes and three different filler contents). The flexural strength and flexural modulus were measured. Three different irregular particle size MRCs without redox-initiator at 94% filler content, as well as amalgam, conventional hybrid composite and Ag-Sn spherical particle MRC were evaluated for condensability. The flexural strength of the Ag-Sn irregular particle MRC was significantly influenced by both the filler particle size and filler contents (p < 0.01). It increased when either the filler content increased or the particles size decreased. The highest flexural strength (97.6 MPa) was obtained from the condition of particles size < 20 microns and 94% filler content. The flexural modulus was significantly influenced by filler content and it increased with increasing filler content. The condensability of the Ag-Sn irregular particle MRC was lower than that of amalgam but much higher than presently available conventional composites and spherical particle MRC.     

Development of metal-resin composite restorative material. Part 2. Effects of acid and heat treatments of silver-tin filler particles on flexural properties of metal-resin composite

The effects of acid and heat treatments of silver-tin filler particles on the flexural properties of metal-resin composite restorative materials were investigated. Five metal-resin composite restorative materials containing different silver-tin filler particles treated under different conditions were experimentally prepared. The conditions of the alloy particles were; 1) as atomized (NT), 2) 1.8% HCl acid-treated (AT), 3) heat-treated at 150 degrees C for 5 min after AT (A15), 4) heat-treated at 200 degrees C for 5 min after AT (A20) and 5) heat-treated at 250 degrees C for 5 min after AT (A25). The flexural strength and the flexural modulus of elasticity were measured for the five metal-resin composites to evaluate the effects of the acid and heat treatments. The flexural strength of the prepared composites was significantly influenced by the surface condition of the filler particles (p < 0.01), and increased significantly when the as atomized particles (NT) were acid-treated (AT) or acid- and heat-treated at 150 degrees C (A15), but then significantly decreased as the heat treatment temperature increased (A20 and A25). The strength of the A15 composite was significantly higher than those of the other composites, and exceeded that (about 60 MPa) of the previous composite with no treatment. No significant difference was found in the flexural modulus of the composites.     

Influence of shade and storage time on the flexural strength, flexural modulus, and hardness of composites used for indirect restorations

STATEMENT OF PROBLEM: Fracture resistance, elastic modulus, and hydrolytic degradation resistance are important properties of indirect composite restorations. Composite systems developed specifically for indirect application are said to have enhanced mechanical properties due to their elevated monomer conversion. PURPOSE: This study evaluated the influence of shade and the effect of 30-day water storage on the flexural strength, flexural modulus, and hardness of 4 commercially available indirect composite systems and 1 composite used with the direct technique. MATERIAL AND METHODS: A variety of commercially available indirect resin composites (Artglass, Belleglass, Sculpture, and Targis) and 1 directly placed composite (Z100, control) were used. Specimens made with either incisal or dentin shade (n = 10) were fractured with a 3-point bending test. Pre-failure loads corresponding to specific displacements of the crosshead were used for flexural modulus calculation. Knoop hardness was measured on fragments (n = 3) obtained after the flexural test. Tests were performed after 24 hours and after a 30-day water storage at 37 degrees C. Flexural strength data were analyzed with the Weibull distribution. Flexural modulus and Knoop hardness data were analyzed with 3-way ANOVA and Tukey's post-hoc test (alpha=0.05). RESULTS: In general, the directly placed composite (Z100) demonstrated flexural strength similar to that of Artglass, Targis, and Sculpture. Belleglass presented the highest flexural strength (221.7 MPa for incisal shade after 24 hours storage; 95% confidence interval: 208.3-235.4). Z100 demonstrated the highest flexural modulus (range: 10.9 +/- 0.6 to 12.0 +/- 0.9 GPa) and Targis the lowest (range: 5.1 +/- 0.5 to 5.9 +/- 0.9 GPa). Sculpture was the only material that showed differences in flexural strength with respect to shade (incisal-24 hours: 149.8 MPa; incisal-30 days: 148.7 MPa; dentin-24 hours: 200.0 MPa; dentin-30 days: 177.9 MPa). The flexural modulus and hardness of the dentin shade of Sculpture were higher than those of the incisal shade after 30 days. Belleglass also showed a significant difference in flexural modulus (dentin-24 hours: 11.1 GPa; incisal-24 hours: 9.6 GPa). The effect of water storage was more evident on hardness since all composite systems softened after 30 days. Prolonged water storage decreased flexural strength only for Artglass-dentin and Z100, both incisal and dentin shades. Water aging did not affect the flexural modulus of any composite tested. CONCLUSION: In general, indirect composites did not show enhanced mechanical properties compared to the directly placed composite. Property differences due to shade were more evident for Sculpture. Prolonged water storage had a deleterious effect on the hardness of all composites tested. However, water storage did not affect the flexural strength of most of the indirect composites or the flexural modulus of any composite tested.     

Flexural strength and moduli of hypoallergenic denture base materials

STATEMENT OF PROBLEM: Hypoallergenic denture base materials show no residual methyl methacrylate (MMA) or significantly lower residual MMA monomer content compared to polymethyl methacrylate-based (PMMA) heat-polymerizing acrylic resin. There is insufficient knowledge of the mechanical properties of hypoallergenic denture base materials to warrant their use in place of PMMA-based acrylic resins for patients with allergic reaction to MMA. PURPOSE: This in vitro study compared flexural strength and flexural modulus of 4 hypoallergenic denture base materials with flexural strength/modulus of a PMMA heat-polymerizing acrylic resin. MATERIAL AND METHODS: The following denture base resins were examined: Sinomer (heat-polymerized, modified methacrylate), Polyan (thermoplastic, modified methacrylate), Promysan (thermoplastic, enterephthalate-based), Microbase (microwave-polymerized, polyurethane-based), and Paladon 65 (heat-polymerized, methacrylate, control group). Specimens of each material were tested for flexural strength and flexural modulus (MPa, n = 5) according to ISO 1567:1999. The data were analyzed with 1-way analysis of variance and the Bonferroni-Dunn multiple comparisons post hoc analysis for each test variable (alpha=.05). RESULTS: Flexural strength of Microbase (67.2 +/- 5.3 MPa) was significantly lower than Paladon 65 (78.6 +/- 5.5 MPa, P <.0001). Flexural strength of Polyan (79.7 +/- 4.2 MPa, P =.599), Promysan (83.5 +/- 3.8 MPa, P =.412), and Sinomer (72.3 +/- 2.1 MPa, P =.015) did not differ significantly from the control group. Significantly lower flexural modulus was obtained from Sinomer (1720 +/- 30 MPa, P =.0007) compared to the PMMA control group (2050 +/- 40 MPa), whereas the flexural modulus of Promysan (2350 +/- 170 MPa, P =.0005) was significantly higher than the PMMA material. Microbase (2100 +/- 210 MPa, P =.373) and Polyan (2070 +/- 60 MPa, P =.577) exhibited flexural modulus similar to the PMMA material. The tested denture base materials fulfilled the requirements regarding flexural strength (>65 MPa). With the exception of Sinomer, the tested denture base resins passed the requirements of ISO 1567 regarding flexural modulus (>2000 MPa). CONCLUSION: Flexural modulus of Promysan was significantly higher than the PMMA material. Microbase and Sinomer exhibited significantly lower flexural strength and flexural modulus, respectively, than PMMA. The other groups did not differ significantly from the control group.     

Influence of veneering composite composition on the efficacy of fiber-reinforced restorations (FRR)

This study investigated the influence of fiber reinforcement on the flexural properties of four commercial (Artglass, Belleglass HP, Herculite XRV and Solidex) veneering composites (Series A) and two experimental composites (Series B&C). This study investigated how the composition of the veneering composites influenced the enhancement of strength and modulus produced by fiber reinforcement. The formulation of the experimental composites were varied by changing the filler load (Series B) or the resin matrix chemistry (Series C) to assess the effect these changes would have on the degree of reinforcement. In Series A, the commercial veneering composites were reinforced by an Ultra-High-Molecular-Weight Polyethylene fiber (UHMW-PE/Connect) to evaluate flexural properties after 24 hours and six months. In Series B, experimental composites with the same organic matrix but with different filler loads (40% to 80% by weight) were also reinforced by Connect fiber to evaluate flexural properties. In Series C, experimental composites (Systems 1-4) with the same filler load (76.5% by weight) but with different organic matrix compositions were reinforced by Connect fiber to evaluate flexural properties. For Series B and C, flexural properties were evaluated after 24 hours water storage. All the samples were prepared in a mold 2 mm x 2 mm x 25 mm and stored in distilled water at 37 degrees C until they were ready for flexural testing in an Instron Universal Testing Machine using a crosshead speed of 1 mm/minute. The results showed no significant differences in the flexural strength (FS) between any of the commercial reinforced composites in Series A. The flexural modulus (FM) of the fiber-reinforced Belleglass HP group was significantly higher than for Artglass and Solidex. Water storage for six months had no significant (p>0.05) effect on the flexural strength of three of the four reinforced veneering composites. The flexural strength for Artglass was significantly reduced (p<0.05) by six-month water storage. In Series B, however, increasing the amount of filler loading improved the flexural modulus of the reinforced experimental composite but had no effect on its flexural strength. In Series C, changing the organic matrix formulation had no affect on flexural strength but affected the flexural modulus of the reinforced experimental composite.     

Laboratory strength of glass ionomer cement, compomers, and resin composites

PURPOSE: The study evaluates the compressive, flexural, and diametral tensile strengths of 8 core build-up materials from different material classes (highly viscous glass ionomer cement, autocured resin composite, and compomers). MATERIALS AND METHODS: All materials were manipulated according to the manufacturers' recommendations for use as core materials. At a temperature of 23.0 +/- 1.0 degrees C the properties of compressive, diametral tensile and flexural strength were determined using a universal testing machine at 15 minutes, 1 hour, and 24 hours after material preparation. Using one-way analysis of variance (ANOVA), multiple mean value comparisons were performed to determine significant differences (p< or =.05) between the core restoration materials. RESULTS: The values for compressive strength varied from 40.3 +/- 5.2 MPa (compomer) to 237.4 +/- 37.3 MPa (autocured resin composite) for the 3 measurement times. At 15 minutes, 1 hour, and 24 hours after first mixing, the ANOVA showed significant differences (p < or =.05) between the resin composite Core Paste and all of the other materials. Diametral tensile strengths ranged from 5.5 +/- 1.1 MPa for glass ionomer cement to 39.1 +/- 2.9 MPa for composite core material. Three-point flexural strength showed values ranging from 12.1 +/- 2.5 MPa for glass ionomer cement to 92.1 +/- 9.7 MPa for compomer between the 3 measurement times. CONCLUSIONS: Setting time influences the mechanical properties of the materials tested in this study. Autopolymerizing resin composite Core Paste demonstrated greater compressive and flexural strengths at the 3 measurement times than the other materials tested. Reinforced composites, in comparison to the autocured resin composites, yielded no improvement in tensile strength. Flexural and tensile strengths of the glass ionomer cement were lower than those of autocured resin composites and compomers.